Bias mechanisms for a rocker arm and lost motion component of a valve bridge

ABSTRACT

Systems for actuating at least two engine comprise a valve bridge operatively connected to the at least two engine valves and having a hydraulically-actuated lost motion component. A rocker arm has a motion receiving end configured to receive valve actuation motions from a valve actuation motion source and a motion imparting end for conveying the valve actuation motions and hydraulic fluid to the lost motion component. The motion receiving end is biased toward the valve actuation motion source. A bias mechanism, supported by either the rocker arm, valve bridge or both, is configured to bias the motion receiving end of the rocker arm and the lost motion component into contact with each other. By maintaining such contact, the bias mechanism helps maintain the supply of hydraulic fluid from the rocker arm to the lost motion component.

CROSS-REFERENCE TO RELATED APPLICATION

The instant application claims the benefit of Provisional U.S. Patent Application Ser. No. 62/024,629 entitled “Valve Bridge With Integrated Lost Motion System” and filed Jul. 15, 2014, the teachings of which are incorporated herein by this reference.

The instant application is also related to co-pending application entitled “System Comprising An Accumulator Upstream Of A Lost Motion Component In A Valve Bridge” having attorney docket number 46115.00.0063, and to co-pending application entitled “Pushrod Assembly” having attorney docket number 46115.00.0064, both filed on even date herewith

FIELD

The instant disclosure relates generally to actuating one or more engine valves in an internal combustion engine and, in particular, to valve actuation including a lost motion system.

BACKGROUND

As known in the art, valve actuation in an internal combustion engine controls the production of positive power. During positive power, intake valves may be opened to admit fuel and air into a cylinder for combustion. One or more exhaust valves may be opened to allow combustion gas to escape from the cylinder. Intake, exhaust, and/or auxiliary valves may also be controlled to provide auxiliary valve events, such as (but not limited to) compression-release (CR) engine braking, bleeder engine braking, exhaust gas recirculation (EGR), internal exhaust gas recirculation (IEGR), brake gas recirculation (BGR) as well as so-called variable valve timing (VVT) events such as early exhaust valve opening (EEVO), late intake valve opening (LIVO), etc.

As noted, engine valve actuation also may be used to produce engine braking and exhaust gas recirculation when the engine is not being used to produce positive power. During engine braking, one or more exhaust valves may be selectively opened to convert, at least temporarily, the engine into an air compressor. In doing so, the engine develops retarding horsepower to help slow a vehicle down. This can provide the operator with increased control over the vehicle and substantially reduce wear on the service brakes of the vehicle.

One method of adjusting valve timing and lift, particularly in the context of engine braking, has been to incorporate a lost motion component in a valve train linkage between the valve and a valve actuation motion source. In the context of internal combustion engines, lost motion is a term applied to a class of technical solutions for modifying the valve motion dictated by a valve actuation motion source with a variable length mechanical, hydraulic or other linkage assembly. In a lost motion system the valve actuation motion source may provide the maximum dwell (time) and greatest lift motion needed over a full range of engine operating conditions. A variable length system may then be included in the valve train linkage between the valve to be opened and the valve actuation motion source to subtract or “lose” part or all of the motion imparted from the valve actuation motion source to the valve. This variable length system, or lost motion system may, when expanded fully, transmit all of the available motion to the valve and when contracted fully transmit none or a minimum amount of the available motion to the valve.

An example of such a valve actuation system 100 comprising a lost motion component is shown schematically in FIG. 1. The valve actuation system 100 includes a valve actuation motion source 110 operatively connected to a rocker arm 120. The rocker arm 200 is operatively connected to a lost motion component 130 that, in turn, is operatively connected to one or more engine valves 140 that may comprise one or more exhaust valves, intake valves, or auxiliary valves. The valve actuation motion source 110 is configured to provide opening and closing motions that are applied to the rocker arm 120. The lost motion component 130 may be selectively controlled such that all or a portion of the motion from the valve actuation motion source 110 is transferred or not transferred through the rocker arm 120 to the engine valve(s) 140. The lost motion component 130 may also be adapted to modify the amount and timing of the motion transferred to the engine valve(s) 140 in accordance with operation of a controller 150. As known in the art, valve actuation motion source 110 may comprise any combination of valve train elements, including, but not limited to, one or more: cams, push tubes or pushrods, tappets or their equivalents. As known in the art, the valve actuation motion source 110 may be dedicated to providing exhaust motions, intake motions, auxiliary motions or a combination of exhaust or intake motions together with auxiliary motions.

The controller 150 may comprise any electronic (e.g., a microprocessor, microcontroller, digital signal processor, co-processor or the like or combinations thereof capable of executing stored instructions, or programmable logic arrays or the like, as embodied, for example, in an engine control unit (ECU)) or mechanical device for causing all or a portion of the motion from the valve actuation motion source 110 to be transferred, or not transferred, through the rocker arm 120 to the engine valve(s) 140. For example, the controller 150 may control a switched device (e.g., a solenoid supply valve) to selectively supply hydraulic fluid to the rocker arm 120. Alternatively, or additionally, the controller 150 may be coupled to one or more sensors (not shown) that provide data used by the controller 150 to determine how to control the switched device(s). Engine valve events may be optimized at a plurality of engine operating conditions (e.g., speeds, loads, temperatures, pressures, positional information, etc.) based upon information collected by the controller 150 via such sensors.

Where the lost motion component 130 is hydraulically actuated, the supply of the necessary hydraulic fluid is of critical importance to the successful operation of the valve actuation system 100. Complicating such hydraulic fluid supply is the existence of lash space (i.e., gaps) between components in a valve train, which may result in separation and impact of adjacent valve train components, resulting in noise or impact damage, or loss of hydraulic fluid supply between such adjacent components. This is particularly true of so-called bridge brake systems in which the lost motion component 130 is supported by or deployed within a valve bridge (not shown) and hydraulic fluid for actuating the lost motion component 130 is supplied via the rocker arm 120.

SUMMARY

The instant disclosure describes systems for actuating at least two engine valves in a valve actuation system comprising a valve bridge operatively connected to the at least two engine valves and having a hydraulically-actuated lost motion component. The systems further comprise a rocker arm having a motion receiving end configured to receive valve actuation motions from a valve actuation motion source and a motion imparting end for conveying the valve actuation motions and hydraulic fluid to the lost motion component. In these systems, the motion receiving end of the rocker arm is biased toward the valve actuation motion source. The systems also comprise a bias mechanism, supported by either the rocker arm, valve bridge or both, that is configured to bias the motion imparting end of the rocker arm and the lost motion component into contact with each other. By maintaining such contact, the bias mechanism helps maintain the supply of hydraulic fluid from the rocker arm to the lost motion component.

In an embodiment, the lost motion component comprises a first piston slidably disposed in a first piston bore formed in the valve bridge. In this instance, the bias mechanism comprises a resilient element operatively connected to the first piston and configured to bias the first piston out of the first piston bore. The resilient element in this embodiment may be disposed within or outside of the first piston bore.

In another embodiment, the motion imparting end of the rocker arm comprises a sliding member disposed within a sliding member bore formed in the motion imparting end of the rocker arm and configured to contact the lost motion component. In this embodiment, the bias mechanism comprises a resilient element operatively connected to the sliding member and configured to bias the sliding member out of the sliding member bore. In this embodiment, the resilient element may be disposed within or outside of the sliding member bore. Further, the rocker arm may comprise a hydraulic passage in the motion imparting end, wherein the hydraulic passage is in fluid communication with the sliding member passage formed in the sliding member. Further still, a lubrication passage may be formed in the motion imparting end and in fluid communication with the sliding member bore.

In all embodiments, the valve bridge may comprise at least one second piston slidably disposed within at least one second piston bore formed in the valve bridge, where the at least one second piston bore is in fluid communication with the first piston bore via at least one hydraulic passage formed in the valve bridge. In this case, each of the at least one second pistons is configured to contact a corresponding engine valve of the at least two engine valves. Further still, the first piston may comprise a cavity and an opening in fluid communication with the cavity, as well as a check valve disposed in the cavity such that hydraulic fluid introduced into the cavity via the opening flows through the check valve into the first piston bore, the at least one hydraulic passage and the second piston bore.

Valve bridges and rocker arms for use in such systems are further described.

BRIEF DESCRIPTION OF THE DRAWINGS

The features described in this disclosure are set forth with particularity in the appended claims. These features and attendant advantages will become apparent from consideration of the following detailed description, taken in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings wherein like reference numerals represent like elements and in which:

FIG. 1 is a block diagram schematically illustrating a valve actuation system in accordance with prior art techniques;

FIG. 2 is a block diagram schematically illustrating a valve actuation system in accordance with the instant disclosure;

FIG. 3 is a cross-sectional view of a valve bridge in accordance with a first embodiment of the instant disclosure;

FIG. 4 is a cross-sectional view of a valve bridge in accordance with a second embodiment of the instant disclosure; and

FIG. 5 is a cross-sectional view of a rocker arm in accordance with a third embodiment of the instant disclosure.

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS

Referring now to FIG. 2, a valve actuation system 200 in accordance with the instant disclosure is illustrated. As shown, the system 200 comprises a valve actuation motion source 110, as described above, operatively connected to a motion receiving end 212 of a rocker arm 210. The rocker arm 210 also comprises a motion imparting end 214 that, as described in further detail below, may be configured to support a bias mechanism 250. The system 200 further comprises a valve bridge 220 operatively connected to the two or more engine valves 140. As known in the art of bridge brake systems, the valve bridge 220 may comprise a lost motion component 230. The valve bridge 240 may also be configured to support a bias mechanism 240 as described in further detail below.

Though not illustrated in FIG. 2, the rocker arm 210 is typically supported by a rocker arm shaft and the rocker arm 210 reciprocates about the rocker arm shaft. Also, as known in the art, the rocker arm shaft may incorporate elements of a hydraulic fluid supply 260 in the form of hydraulic fluid passages formed along the length of the rocker arm shaft. As further known in the art, the motion receiving end 212 may comprise any of a number of suitable configurations depending on the nature of the valve actuation motion source 110. For example, where the valve actuation motion source 110 comprises a cam, the motion receiving end 212 may comprise a cam roller. Alternatively, where the valve actuation motion source 110 comprises a push tube, the motion receiving end 212 may comprise a suitable receptacle surface configured to receive the end of the push tube. The instant disclosure is not limited in this regard.

As shown, the motion imparting end 214 of the rocker arm 210 conveys valve actuation motions (solid arrows) provided by the valve actuation motion source 110 to the lost motion component 230 of the valve bridge 220. Though not shown in FIG. 2, one or more hydraulic passages are provided in the motion imparting end 214 of the rocker arm 210 such that hydraulic fluid (dotted arrows) received from the hydraulic fluid supply 260 may also be conveyed to the lost motion component 230 via the motion imparting end 214. As further illustrated below, the motion imparting end 214 may comprise one or more components, in addition to the body of the rocker arm 210 itself, that facilitate the conveyance of the valve actuation motions and hydraulic fluid to the lost motion component 230.

In all embodiments described herein, the motion receiving end 212 of the rocker arm is biased toward the valve actuation motion source 110 as schematically indicated by a rocker bias force 126. Though illustrated as being applied to the upper portion of the motion receiving end 212 in FIG. 2, manner in which the bias force 126 is established may vary as a matter of design choice. Thus, for example, the bias force 126 could be applied to the lower portion of the motion imparting end 214, thereby biasing the motion receiving end 212 in the direction of the valve actuation motion source 110.

The valve bridge 220 operatively connects to two or more engine valves 140 that, as noted previously, may comprise intake valves, exhaust valves and/or auxiliary valves, as known in the art. The lost motion component 230 is supported by the valve bridge 220 and is configured to receive the valve actuation motions and hydraulic fluid from the motion imparting end 214 of the rocker arm 210. The lost motion component 230 is hydraulically-actuated in the sense that the supply of hydraulic fluid causes the lost motion component 230 to either assume a state in which the received valve actuation motions are conveyed to the valve bridge 220 and, consequently, the valves 140, or a state in which the received valve actuation motions are not conveyed to the valve bridge 220 and are therefore “lost.” An example of a lost motion component in a valve bridge is taught in U.S. Pat. No. 7,905,208, the teachings of which are incorporated herein by this reference, in which valve actuation motions from the rocker arm are lost when hydraulic fluid is not provided to the lost motion component, but are conveyed to the valve bridge and valves when hydraulic fluid is provided to the lost motion component. In lost motion components 230 of this type, a check valve (not shown) is provided to permit one-way flow of hydraulic fluid into the lost motion component 230. The check valve permits the lost motion component 230 to establish a locked volume of hydraulic fluid that, due to the substantially incompressible nature of the hydraulic fluid, allows the lost motion component 230 to operate in substantially rigid fashion thereby conveying the received valve actuation motions.

An aspect of both types of above-mentioned lost motion components 230 is that application of hydraulic fluid to the lost motion component is required in order to switch the lost motion component into a motion-conveying or motion-losing state. However, as noted above, the motion receiving end 212 of the rocker arm 210 is biased toward the valve actuation motion source 110 and, consequently, the motion imparting end 214 of the rocker arm is biased away from the lost motion component 230. Biasing of the rocker arm 210 in this manner results in lash space between the motion imparting end 214 of the rocker arm and the lost motion component 230. However, the existence of such lash space may result in the interruption of the provision of hydraulic fluid between the motion imparting end 214 of the rocker arm 210 and the lost motion component 230, which could likewise interrupt proper operation of the lost motion component 230.

In order to overcome the effects of such lash space, one or more bias mechanisms 240, 250 may be supported by the valve bridge 220 and/or rocker arm 210. The bias mechanisms 240, 250 are configured to bias the motion imparting end 214 of the rocker arm 210 and the lost motion component 230 into contact with each other and, in doing so, preserving the fluid communication between the motion imparting end 214 and the lost motion component 230. Thus, in one embodiment, a bias mechanism 240 supported by the valve bridge 220 causes the lost motion component 230 (or a portion thereof) to be biased into contact with the motion imparting end 214 of the rocker arm 210. Alternatively, in another embodiment, a bias mechanism 250 supported by the rocker arm 210 causes the motion imparting end 214 (or a portion thereof) to be biased into contact with the lost motion component 230. Further still, it may be desirable in some situations to provide the bias mechanisms 240, 250 in both the valve bridge 220 and rocker arm 210.

Regardless, the bias mechanisms 240, 250 taught herein are preferably configured to maintain fluid communication between the motion imparting end 214 and the lost motion component 230, i.e., they provide enough biasing force to maintain the fluid communication despite movement of the rocker arm 210 and valve bridge 220. In presently preferred embodiments, the bias mechanisms 240, 250 may be take the form of resilient elements such as springs or equivalents thereof. Various embodiments of valve bridges and rocker arms in accordance with the instant disclosure are further illustrated below with respect to FIGS. 3-5.

Referring now to FIG. 3, a valve bridge 300 is illustrated having a first piston 302 slidably disposed in a first piston bore 304 formed in the valve bridge 300. The first piston 302 and first piston bore 304 are configured, as described above, to receiving valve actuation motions and hydraulic fluid from the motion imparting end 214 of the rocker arm 210 (not shown). The first piston 302 may comprise an opening 306 providing fluid communication with a cavity 308 formed within the first piston 302. A check valve assembly comprising a check valve 310, check valve spring 312 and check valve retainer 314 are provided within the cavity 308. As described above, the check valve assembly permits one-way fluid communication from the motion imparting end 214 of the rocker arm 210 to the cavity 308 and first piston bore 304.

As further shown in FIG. 3, a second piston 330 may be slidably disposed within a second piston bore 332 formed in the valve bridge 300. The second piston 330 and second piston bore 332 are configured to align with an engine valve such that an end of the engine valve may be received in a corresponding receptacle 336 formed in the second piston 330. A second piston spring 334 is provided to bias the second piston 330 in a direction toward its corresponding engine valve. Further still, a hydraulic passage 340 (partially shown) is provided between the first piston bore 304 and the second piston bore 332. As known in the art, when the cavity 308, first piston bore 304, hydraulic passage 340 and first piston bore 332 are charged with hydraulic fluid, the first piston 302 and the second piston 330 act as master and slave pistons, respectively, such that valve actuation motions received by the first piston 302 are conveyed to the second piston 330 and it corresponding engine valve. As further shown, a receptacle 350 is provided on an end of the valve bridge opposite the second piston 330 such that the receptacle aligns with (and is configured to receive an end of) another engine valve (not shown). When the cavity 308, first piston bore 304, hydraulic passage 340 and first piston bore 332 are not charged with hydraulic fluid, travel of the first piston 302 is limited by shoulders 360 formed in the first piston bore 304. It is noted that yet another second piston and hydraulic passage arrangement could be provided in the place of the receptacle 350 such that the first piston 302 is capable of serving as a master piston to two slave pistons, rather than only one as illustrated in FIG. 3.

As further shown in FIG. 3, a resilient element 320 is disposed within the first piston bore 304 and operatively connected to the first piston 302, in this instance, via the check valve retainer 314 that is affixed to the first piston 302. As configured, the resilient element 320 biases the first piston 302 out of the first piston bore 304 and, consequently, into contact with the motion imparting end 214 of the rocker arm 210. Preferably, the resilient element 320 provides a sufficient force to maintain contact between the first piston 302 and the motion imparting end 214 of the rocker arm 210 despite movements thereof. However, the force provided by the resilient element 320 is also preferably chosen to be relatively easily overcome by the force of any valve actuation motions applied to the first piston 302, thereby preventing excessive loading on the rocker arm 210 and upstream valve train components.

An alternative embodiment of the valve bridge of FIG. 3 is illustrated in FIG. 4. In particular, the embodiment of FIG. 4 is substantially the same as the embodiment of FIG. 3, with the exception that the first piston 302 comprises a lip 402 that engages a resilient element 404 disposed outside of the first piston bore 304. As illustrated, the resilient element 404, comprising a conventional compression spring, surrounds the first piston 302 in this embodiment. As will be appreciated by those skilled in the art, other types of springs, such as leaf springs or the like, could be equally employed as the resilient elements in the embodiments of FIGS. 3 and 4. Regardless, the resilient element 404 is once again chosen to provide the desired contact between the first piston 302 and the motion imparting end 214, which biasing force is readily overcome by the valve actuation motions. In yet another embodiment, resilient elements could be disposed both within and outside of the first piston bore, in effect combining the implementations illustrated in FIGS. 3 and 4.

In both FIGS. 3 and 4, the valve bridge 300 further comprises a reaction surface 370 having a bleed passage 372 formed therein. The bleed passage 372 is in fluid communication with the second piston bore 332 and, consequently, the hydraulic passage 340. As known in the art, the valve bridge 300 is biased against a reaction load screw or similar structure (not shown) that serves to seat against the reaction surface 370 when the first piston 302 is conveying motion to the engine valves via the second piston; the pressure created in the second piston bore 332 in this circumstance causes the valve bridge 300 to displace upward such that the bleed passage 372 is sealed and any hydraulic fluid present in the second piston bore 332 and hydraulic passage 340 is substantially prevented from leaking out. When a sufficiently high lift valve event (e.g., a main exhaust event) is applied to the rocker arm contacting the valve bridge 300, further translation of the second piston 330 will not be possible (as limited, for example, by the shoulder 360 within the second piston bore 304). As a consequence, the valve bridge 300 will displace under the urging of the rocker arm, thereby causing reaction surface 372 to unseat from the reaction load bolt. As a result, the bleed passage 372 will be unsealed, thereby permitting the pressurized hydraulic fluid in the second piston bore 372, hydraulic passage 340 and first piston bore 304 to rapidly escape. This discharge of hydraulic fluid then permits the second piston 330 to translate back into the second piston bore 332, thereby preventing the high lift valve motion from being conveyed to the engine valve.

Referring now to FIG. 5, an embodiment in which the bias mechanism is disposed in a rocker arm 502 is further illustrated. In particular, the rocker arm 502 comprises a motion imparting end 504, as described above, and a rocker shaft bore 520 configured to receive a rocker shaft (not shown). A hydraulic passage 522 is formed in the motion imparting end 504 of the rocker arm 502, an end of which is configured to fluidly communicate with a hydraulic fluid supply, such as rocker shaft hydraulic passages as known in the art. Such fluid supply for the valve bridge is typically switched (via a solenoid supply valve, for example) that permits pressure within the hydraulic passage 522 to be increased or decreased in order to control operation of the lost motion component.

The motion imparting end 504 further includes a sliding assembly 506 comprising a sliding member 506 slidably disposed in a sliding member bore 508 formed in the motion imparting end 504. As shown, the sliding assembly 506 is formed in a distal portion of the motion imparting end 504, though the particular location of the sliding assembly 506 within the motion imparting end 504 may be selected as a matter of design choice provided that it is configured to contact the lost motion component of a valve bridge as described above. The sliding member bore 508 is in fluid communication with the hydraulic passage 522. In turn, the sliding member 506 also comprises a sliding member passage 510 such that hydraulic fluid is able to flow from the hydraulic passage 522 into the sliding member bore 508 and through the sliding member passage 508. In order to ensure solid contact between the rocker arm 502 and the sliding member 506 when conveying valve actuation motions, the sliding member 506 comprises a shoulder 512 that serves as a hard stop to restrict upward movement of the sliding member 506 within the sliding member bore 508. As further shown in FIG. 5, the motion imparting end 504 of the rocker arm 502 may comprise a lubrication passage 524 formed therein and configured for fluid communication with a hydraulic fluid supply and the sliding member bore 508. As shown, the lubrication passage 524 intersects with the sliding member bore 508 so that leakage is limited by the clearance between the sliding member 506 and the bore 508. In contrast to the switched fluid supply used in conjunction with the hydraulic passage 522, the fluid supplied to the lubrication passage 524 is preferably always pressurized in order to maintain consistent lubrication.

In keeping with known techniques, an end of the sliding member 506 extending out of the sliding member bore 508 may be formed with a substantially spherical surface thereby permitting coupling of the sliding member 506 with a so-called swivel or elephant foot 514. As known in the art, the swivel foot 514 accommodates relative movement between the rocker arm 502 and valve bridge while still providing fluid communication with the sliding member passage 510 via an opening 516 formed in the swivel foot 514.

Finally, a resilient element 518, in the form of a compression spring, is disposed within the sliding member bore 508 such that the resilient element 518 consistently biases the sliding member 506 out of the sliding member bore 508. Once again, as with the embodiment of FIGS. 3 and 4, the resilient element 518 is chosen to provide the desired contact between the sliding assembly 506 and the lost motion component of the valve bridge, which biasing force is readily overcome by the valve actuation motions.

Similar to the embodiment of FIG. 4, the resilient element 508 need not be disposed within the sliding member bore 508 in all instances, and may be disposed outside of the sliding member bore 508 in some implementations. For example, the resilient element, in the form of a suitable spring, could be placed between the shoulder 512 of the sliding member 506 and a complementary surface of the motion imparting end 504.

Further still, as noted above, it may be desirable to combine embodiments of the type illustrated in FIGS. 3 and 4 with embodiments of the type illustrated in FIG. 5. In these instances, the resilient elements 320, 404, 518 may be chosen to account for the fact that multiple such resilient elements are used, thereby permitting the possible reduction in the force provided any one of the resilient elements.

While particular preferred embodiments have been shown and described, those skilled in the art will appreciate that changes and modifications may be made without departing from the instant teachings. It is therefore contemplated that any and all modifications, variations or equivalents of the above-described teachings fall within the scope of the basic underlying principles disclosed above and claimed herein. 

What is claimed is:
 1. A system for actuating at least one of two or more engine valves in an internal combustion engine, the system comprising: a valve bridge operatively connected to the two or more engine valves, the valve bridge comprising a hydraulically-actuated lost motion component; a rocker arm having a motion receiving end configured to receive valve actuation motions from a valve actuation motion source and a motion imparting end configured to convey the valve actuation motions and hydraulic fluid to the lost motion component, wherein the motion receiving end of the rocker arm is biased toward the valve actuation motion source; and a bias mechanism supported by at least one of the rocker arm and the valve bridge configured to bias the motion imparting end of rocker arm and the lost motion component into contact with each other.
 2. The system of claim 1, wherein the bias mechanism is configured to maintain hydraulic communication between the rocker arm and the lost motion component.
 3. The system of claim 1, the lost motion component of the valve bridge comprising a first piston slidably disposed in a first piston bore formed in the valve bridge, wherein the bias mechanism comprises: a resilient element operatively connected to the first piston and configured to bias the first piston out of the first piston bore.
 4. The system of claim 3, wherein the resilient element is disposed within the first piston bore.
 5. The system of claim 3, wherein the resilient element is disposed outside of the first piston bore.
 6. The system of claim 3, the valve bridge further comprising: at least one second piston slidably disposed in at least one second piston bore formed in the valve bridge, the at least one second piston bore in fluid communication with the first piston bore via at least one hydraulic passage formed in the valve bridge.
 7. The system of claim 6, wherein each of the at least one second piston is configured to contact a corresponding engine valve of the two or more engine valves.
 8. The system of claim 6, the first piston further comprising a cavity and an opening communicating with the cavity, the system further comprising: a check valve disposed in the cavity, wherein hydraulic fluid introduced into the cavity through the opening flows through the check valve and into the first piston bore, the at least one hydraulic passage and the at least one second piston bore.
 9. The system of claim 1, wherein the motion imparting end comprises: a sliding member, disposed within a sliding member bore formed in the motion imparting end of the rocker arm, configured to contact the lost motion component; and wherein the bias mechanism comprises: a resilient element operatively connected to the sliding member and configured to bias the sliding member out of the sliding member bore.
 10. The system of claim 9, further comprising a hydraulic passage formed in the motion imparting end of the rocker arm, the sliding member further comprising a sliding member passage in fluid communication with the hydraulic passage.
 11. The system of claim 9, further comprising a lubrication passage formed in the motion imparting end of the rocker arm and in fluid communication with the sliding member bore.
 12. The system of claim 9, wherein the resilient element is disposed within the sliding member bore.
 13. The system of claim 9, wherein the resilient element is disposed outside of the sliding member bore.
 14. A valve bridge configured to be operatively connected to at least two engine valves of an internal combustion engine, the valve bridge further comprising: a lost motion component comprising a first piston slidably disposed in a first piston bore formed in the valve bridge and configured to receive valve actuation motions provided by a valve actuation motion source; and a resilient element operatively connected to the first piston and configured to bias the first piston out of the first piston bore.
 15. A rocker arm having a motion receiving end configured to receive valve actuation motions from a valve actuation motion source and a motion imparting end configured to convey the valve actuation motions to a valve bridge that is configured to be operatively connected to at least two engine valves of an internal combustion engine, the rocker arm further comprising: a sliding member, disposed with a sliding member bore formed in the motion imparting end of the rocker arm, configured to contact the valve bridge; and a bias mechanism operatively connected to the sliding member and configured to bias the sliding member out of the sliding member bore. 